Observation of the circular polarization correlation of the positron-electron annihilation quanta

The circular polarization-circular polarization angular correlation of annihilation quanta has been measured unambiguously by use of two backscattering Compton polarimeters in coincidence. The interpretation of the measurement required a quantum mechanical calculation of the circular polarization detection probability for coincident annihilation quanta. This calculation showed that the most favourable geometry for detecting a circular polarization correlation is the backscattering geometry because here, in contrast to forward scattering and transmission geometries, strong perturbations by the linear polarization correlation are not present. By using the polarization efficiencyη=4.7% for a single polarimeter, which was derived from a Monte Carlo calculation, the measured effect for the circular polarization-circular polarization correlation showed good agreement with theory.     

Analysis of the Polarization Influence on the Erbium-Doped Fiber Laser Transient Behavior

Abstract

We studied the erbium-doped fiber laser transient behavior dependence on the pump polarization state or on the cavity polarization eigenvalues. Several series of measurements are shown in which the changes in the transient laser response can be appreciated as the pump polarization state, or the cavity polarization eigenvalues are modified by means of polarization controllers. Results are fitted to a model considering polarization hole burning. It is shown that including this effect is fundamental for a correct erbium-doped fiber laser transient model. On the other hand, the validity of the model's fitting parameters under pump or cavity polarization changes is analyzed.     

利用偏振度研究散射介质浓度及杂质比的数值分析

为了研究散射介质的粒子数浓度对散射光偏振度的影响以及杂质混合比与目标偏振度的关系,求解了当激光器输出波长处于近红外波段806 nm时目标的米勒矩阵及偏振度的数值解,结果表明偏振度随散射介质粒子数浓度的变化十分显著;通过建立混合目标模型,讨论了杂质比与偏振度的数值关系,并对目标的偏振度进行了归一化,而且实现了由归一化偏振度对杂质混合比的反演。本文的研究结果为利用散射光偏振度研究大气遥感提供了新的途径。     

Fluctuations of the polarization state of laser light

The instantaneous polarization of a laser fluctuates between different elliptical states resulting in a partial polarization. The fluctuations are calculated for a laser with partial linear polarization from the known statistical distributions of the amplitude and phase of laser light. A mean square deviation of the polarization direction of 5 s of arc results for a typical He-Ne-laser.     

光源偏振度对光纤陀螺零漂影响的研究

以Y波导集成光学调制器保偏型干涉式光纤陀螺作为研究对象,根据各光学元器件的参数建立了各器件的琼斯矩阵以及光路传输模型,在此基础上进行了光路偏振误差的理论分析。通过推导,得到了保偏型干涉式光纤陀螺的偏振误差表达式,并首次分析了光源偏振度对光纤陀螺零漂的影响。借助光源尾纤输出的光谱,对由0%~3%之间呈线性变化的偏振度以及对经实验测试的光源偏振度的实际值引起的偏振模式耦合误差的零漂值进行了仿真计算。结果表明,当光路中其它参数不变时,由光源偏振度变化引起的零漂值为0.001°/h,满足了高精度光纤陀螺的精度要求。     

Fluctuations of the polarization state of laser light

The instantaneous polarization of a laser fluctuates between different elliptical states resulting in a partial polarization. The fluctuations are calculated for a laser with partial linear polarization from the known statistical distributions of the amplitude and phase of laser light. A mean square deviation of the polarization direction of 5 s of arc results for a typical He-Ne-laser.     

Photon energy dependence of the spin polarization

Spin polarization in semiconductors was investigated by pump-probe measurements, where the transmissions of the samples were monitored with probe pulses with same and opposite circular polarizations. The spin polarization as a function of the pump-probe delay was estimated, and the polarization was found to decay in a sub-ns timescale. It was also found that the polarization depends strongly on photon energy of the pump beam. The pumping energy dependence of the spin polarization was discussed based on the inter-band transition probabilities.     

The impact of the orientation angles uncertainty of instrument polarizers on polarization measurement accuracy

Improving the polarimetric measurement accuracy of the polarization CCD camera is a fundamental task in the remote sensing of the earth. This paper presents a simple approach for estimating the degree of polarization errors caused by the orientation angles uncertainty of the instrument polarizers. We show that the measured degree of polarization error for a certain orientation angle of the instrument polarizers in the same spectral band depends on the polarization state (polarization angle or degree of polarization) of the incident light. In order to evaluate the polarimetric measurement performance of the instrument, the average degree of polarization error is defined based on the assumption that the incident light beams have equal polarization angle probability. The simulated test showed that the average degree of polarization errors of the 3 polarized spectral bands in the airborne polarization CCD camera is nearly equal because of the same orientation angles uncertainty of the instrument polarizers, though the instrument polarizers in the 3 polarized spectral bands are equipped a little differently; the instrument often encounters a large average degree of polarization errors for the large degree of polarization of the incident beams.     

The study of the weibel electromagnetic instability growth rate in the presence of the body stress

Body stress flow can be expected in the fast ignition imploding of the inertial fusion process that strongly damps small‐scale velocity structures. The Weibel instability is one of the plasma instabilities that require anisotropy in the distribution function. The body stress effect was neglected in the calculation of the Weibel instability growth rate. In this article, the propagation condition of impinging waves and the growing modes of the Weibel instability on the plasma density gradient of the fuel fusion with the body stress flow are investigated. Calculations show that the minimum value of the body stress rate threshold in the linear polarization is about 2.96 times greater than that of the circular polarization. Increasing 10 times of the density gradient and decreasing 2 times of the wavelength in the linear polarization and the circular polarization, respectively, lead to about 1.78 × 10⁶ times increment and 0.019 times decrement in the maximum of the Weibel instability growth rate. Also, the Weibel instability growth rate maximum in the circular polarization is about 10⁷ times greater than that of the linear polarization. The body stress flow and the density gradient tend to stabilize the Weibel instability in the circular polarization and act as a destabilizing source in the linear polarization. Therefore, by increasing steps of the density gradient plasma near the relativistic electron beam‐emitting region, in the circular polarization, the Weibel instability occurs at a higher stress flow.     

Transformation of the polarization structure of laser radiation in optical systems

A range of questions regarding the calculation of the spatial polarization structure of laser radiation in optical systems is considered. It is shown that polarization aberrations in such systems lead to a distortion of the initial polarization structure. Requirements for an optical system intended for the transmission of the polarization structure of laser radiation and methods for the compensation of polarization aberrations are discussed.     

基于互补屏的极化分离结构设计研究

以互补频率选择表面 (CFSS)结构的强耦合作用为基础, 设计一种具有极化分离作用的频率选择表面 (PSS), 当容性表面与感性表面沿周期排布方向具有横向位移时, CFSS成为具有TM带通、TE带阻的极化分离结构. 建立等效电路模型分析PSS结构极化分离原理, 采用耦合积分方程法计算极化分离结构的传输特性以及容性表面和感性表面的电场分布. 理论分析与实验测试结果均表明: PSS具有良好的极化分离特性和角度稳定性, 为极化波产生器和极化分离结构的设计提供借鉴. 关键词： 频率选择表面 极化选择 互补屏频率选择表面     

海面太阳耀光背景下的偏振探测技术

为了实时抑制太阳耀光对海面目标探测的影响,基于偏振光学理论,设计并构建了一套偏振自适应滤波探测系统。本文介绍了偏振探测系统的功能和组成、偏振探测及背景抑制原理,并给出了该系统的光学设计结果;利用自适应偏振滤波探测系统,通过搭载望远镜跟踪试验平台,针对海上典型目标,开展了相关的偏振验证实验。实验结果表明:海面太阳耀光存在比较明显的偏振特性,采用常规探测手段,探测器极易出现饱和,而利用偏振探测技术则能够有效抑制太阳耀光的影响,进而实现目标的有效探测。     

基于偏振菲涅尔反射比分布的主动偏振成像目标辨别方法

由于偏振特性是材料自身所决定的物理特性,其偏振图像含有丰富的目标信息,利用偏振信息对目标进行识别一直是国内外目标探测领域的研究热点,而主动偏振成像较之被动偏振成像更具有信噪比高以及可控性好等优势。在详细分析了偏振菲涅尔反射比分布的理论基础上,提出了一种利用探测物体表面的偏振菲涅尔反射比的主动偏振成像方法。该方法在发射端将偏振方向正交的两种偏振态的光源交替照射到目标场景中,在探测端用分别装有两个偏振方向垂直的偏振片的CCD采集偏振图像。同时,将探测端架构在不同的探测方向采集目标经主动光源照射后的偏振数据,最后将这些数据传输到计算中心,通过最优化拟合技术反演出不同目标的光学常数,由于不同目标的表面材质不同,其反映出的光学常数就不同,从而达到辨识不同材质目标的目的。实验分别采用了仿真数据和实测数据来验证该方法的有效性。仿真实验显示,所提出的方法利用材料的光学常数对不同材料进行区分不仅是科学的而且更方便有效。实测数据进一步验证了该方法能够较好的恢复出目标的相关光学常数,尤其在区分金属和非金属材料方面表现突出,并且探测方法结构简单实用,在目标探测、伪装识别等领域中有较大应用前景。     

On the optimum set of polarization measurements for the scattering of two indentical fermions to determine the helicity amplitudes

The polarization asymmetries related to usual polarizations combine at least 4 different helicity amplitudes. The introduction of ±45° inclined transverse polarizations allows us to obtain the complete set of new polarization asymmetries combining only up to 3 helicity amplitudes. There are no further polarization asymmetries depending on a smaller number of helicity amplitudes. These expressions are most economical to determine the helicity amplitudes from observed data. Some of them are suitable to study especially the spin-flip effects. We give a complete Table of all such polarization asymmetries.     

Experimental investigation of the effect of conducting fractal phases on the permittivity of composites

The dependence of the permittivities of a number of model systems on the bulk resistivity is studied experimentally. The effect of fractal polarization is considered on the basis of analysis of experimental data. A qualitative model of relaxation phenomena is proposed for a new type of surface polarization that can be treated as a logical continuation of the Maxwell-Wagner polarization to conducting filters.     

Control of the polarization properties of the supercontinuum generation in a noncentrosymmetric crystal

A systematic experimental study on the polarization properties of supercontinuum generation (SCG) in a noncentrosymmetric crystal (KDP) is reported. Our studies show that depolarization of the SCG is dependent on the plane of polarization of incident light as well as on the orientation of the crystal, allowing a better control of the polarization properties.     

不同融化状态雪的偏振特性分析

在当今全球变暖的形势下,传统对于固态雪的研究已无法满足需求,文章定性分析了不同融化状态雪的偏振反射光谱,重点探讨了偏振角、方位角、光线入射天顶角和探测天顶角与不同融雪类型的关系,发现这些因素对不同融雪类型的偏振反射光谱均有影响。在可见光波段,融雪在90°偏振时的反射比最大,0°偏振时最小;探测角与入射角越大时,融雪的偏振反射比也越大;不同方位角时的融雪偏振反射光谱出现异于其他地物光谱的反常现象;某些波段的偏振光谱特征对判断融雪含水量大小具有一定意义;同时随着含水量的增加偏振反射比显著下降。这些规律为以后利用偏振光谱定量分析融雪特性奠定了基础,同时在淡水资源管理和监测春汛等自然灾害方面也有一定的现实意义。     

Mechanism of Polarization Production by Means of the Tilted-Foil Technique Studied Using Beta-Radioactive Nuclei

In order to disclose the polarization mechanism of the tilted-foil technique, systematic experimental studies were performed through direct observations of the nuclear polarization of short-lived beta-emitters. The present studies concentrated on the mechanisms of the following processes: (1) production of atomic polarization in the beam–tilted-foil interaction, (2) polarization transfer between an atom and a nucleus, and (3) enhancement of nuclear polarization by the beam multi-tilted-foil interaction. The present results have confirmed the plausibility of a previous model in which the atomic-polarization process in the tilted-foil technique is attributed to the right–left asymmetry of the electron-capture process at the final surface of a tilted foil. The enhancement effect of nuclear polarization by the multi-tilted-foil technique could be consistently explained by a model proposed by Goldring and Niv. Further information on atomic processes is required to make a definite statement on hyperfine interactions and atomic configurations, which contribute to polarization transfer.     

腔内偏振元件对激光特性的影响

Nd:YAG固体激光器的偏振特性在许多实际应用中非常重要.特别是在非线性光学频率变换中,无论是实现Ⅰ类相位匹配还是Ⅱ类相位匹配的非线性光学晶体,对基频光的偏振特性都有一定的要求.研究了半导体激光侧向泵浦固体Nd:YAG激光器的偏振特性.实验测量了腔内镀膜偏振片和它们在腔内不同位置时对激光偏振特性的影响.消光比测量表明,...